During the course of radiation therapy, radiation-induced chronic morbidities may be observed in nearby critical structures. For younger patients and for patients with longer life expectancy, RT-induced second malignancies will likely increase. Curative doses of radiation in many instances may lead to good disease control but cause radiation-induced chronic morbidities in treatment areas. These include interstitial capillary injury of the myocardium leading to an increased incidence of coronary artery disease, cardiomyopathy, and pulmonary interstitial fibrosis, which could occur during lung or breast treatments. These toxicities are dose related, and reducing the radiation damage to nearby critical structures is highly desirable and very relevant to the patient's quality of life.
There is a large body of data in literature on tissue tolerances which shows it is important to respect the tolerance of critical structures such as the heart, lungs, esophagus, etc., and reduce associated morbidities while improving the quality of life. In most clinical situations, the radiation oncologist compromises the upper level of achieving specific tumoricidal dose to the tolerance doses of the nearby normal tissues. With the advent of Intensity-Modulated Radiation Therapy (IMRT) as a new radiation modality, some relief in sparing critical organs has been achieved as this technique has the potential to increase the therapeutic ratio. However, with newer treatments of stereotactic body radiotherapy (SBRT) for many disease sites, where in a smaller number of fractions a much larger dose per fraction is delivered, there are times when normal tissue located in the vicinity or path of the beam has to be sacrificed.
As an example, for cancers of the pelvis such as prostate cancer, the rectum is a key dose-limiting structure. Increased rectal dose can lead to acute proctitis, potential serious late toxicities, chronic irritation, bleeding, and ulceration. Currently, there is no easy or effective solution to place a distance between the rectum and the field of radiation. This is true for conventional EBRT, image-guided IMRT, and high dose rate (HDR) brachytherapy. Lowering dose to rectal tissue in newer modalities, such as SBRT with low fractionation and much higher dose per fraction, is of even greater importance. SBRT has rapidly gained acceptance in the radiation oncology community for a number of excellent incentives from the patient's point of view, including a non-invasive treatment, and a shorter treatment course compared to conventional EBRT. From the physician's perspective, SBRT of prostate offers cancer control rates equivalent to those of brachytherapy, conventional external beam IGRT, or surgery.
With HDR treatment of prostate, cervical, and endometrial cancer as well, where a strong radioactive source is often positioned to dwell in the vicinity of the rectum, displacing the anterior rectal wall even a short distance is highly desirable.
No minimally invasive device currently exists that relocates the rectum away from the field of radiation. A known method involves the injection of a biodegradable spacer between the prostate and the rectum. However, the biodegradable spacer is a gel that takes an average of 6 to 12 months to absorb after the injection. Furthermore, with current prostate fixation methods, such as a rectal balloon, the rectum wall anterior is still exposed to higher doses of radiation than desired.
It would be advatangeous to discover devices, systems, and methods for repositioning critical structures, such as the rectum, during radiation therapy treatments.